“Worms” in peaches can mean three different insects, and each one is sprayed at a different time. The white grubs inside the fruit are usually plum curculio larvae. Caterpillars that kill shoot tips and later tunnel into fruit are Oriental fruit moth. Grubs that chew under the bark at the base of the trunk, leaving gummy, sawdust-filled ooze, are peachtree borers. Spraying at the wrong time does little, so identify the pest first.

Table of Contents

The short answer: for worms in the fruit, the key spray window starts right after the petals fall: Mississippi State and Clemson recommend insecticide cover sprays from petal fall to control plum curculio, never during bloom. For peachtree borers in the trunk, spray the lower trunk when eggs are being laid in summer (around early July in Colorado, August in South Carolina). Always read and follow the product label.

Which worm do you have?

Where you see it	What it looks like	Likely pest
Inside the fruit, often with crescent-shaped scars on the skin	Legless, yellowish-white grub up to 1/2 inch	Plum curculio
Wilting, dying shoot tips in spring, then holes in fruit with gummy frass	Pinkish caterpillar up to 1/2 inch, with legs	Oriental fruit moth
Base of the trunk, near or below the soil line	Gum mixed with sawdust-like frass; creamy grub about 1 inch	Peachtree borer
Trunk and main limbs higher up	Gummy ooze with frass	Lesser peachtree borer

Plum curculio

Clemson Extension describes the adult as a mottled brown, 1/4-inch weevil with a long, curved snout. The female cuts a crescent-shaped slit in young fruit to lay eggs, and the grubs feed inside and make the fruit worthless. Mississippi State Extension calls it one of the most damaging pests of homegrown peaches and plums and says its white, legless grubs are the “worms” so often found in unprotected fruit.

Adults overwinter in leaf litter and become active about the time peaches bloom. Clemson describes a simple check: lay a light-colored sheet under the tree and shake the branches. Curculios fold their legs and drop, and they are easy to see on the sheet.

Oriental fruit moth

Clemson says the first generation of caterpillars bores into new shoot tips, which wilt (“flagging”) and die back. Later in the season, once the shoot tips harden, caterpillars move into the fruit, where sprays cannot reach them. Mississippi State notes that infested fruit may show masses of gummy sap and frass at the entry point.

Peachtree borers

Colorado State University Extension calls the peachtree borer the most destructive insect pest of peach and other stone fruits in Colorado. The larvae chew under the bark of the lower trunk and larger roots, and Clemson notes that young trees can be killed by very few larvae. Look for gummy sap mixed with sawdust-like frass at the base of the tree. CSU points out that amber gum without wood particles may instead be cytospora canker, a fungal disease. For more on telling these apart, see why a peach tree oozes sap.

When to spray for worms in the fruit

Timing is everything for curculio and fruit moth.

Do not spray during bloom. Mississippi State says to protect bees and other pollinators by avoiding insecticides while trees are in bloom, and Clemson agrees: do not spray insecticides during bloom.
Start right after petal fall. Mississippi State recommends beginning cover sprays as soon as petals fall to kill overwintered curculios before they lay eggs, and repeating on a 10 to 14 day schedule, tightening it in rainy periods. Clemson also recommends spraying immediately after petals fall for the first generation of curculio.
Keep cover sprays going into summer. Clemson describes additional sprays in mid-June, late June and early July in South Carolina to control the second generation.

For homeowners, both Clemson and Mississippi State list malathion as a key product for plum curculio. Clemson also lists permethrin, esfenvalerate and carbaryl, and many all-purpose home fruit sprays combine an insecticide with a fungicide. Clemson notes that repeated permethrin use may increase scale or spider mite problems later. Each product has a waiting period before harvest; Clemson lists 7 days for malathion and permethrin. Check your own label, since products and rules change.

For Oriental fruit moth, Clemson suggests pheromone traps to tell when moths are active, and treating with permethrin or malathion when catches average more than 10 moths per trap. Mississippi State says good cover sprays for curculio usually help with fruit moth too.

For a broader schedule that includes disease sprays, see what to spray on peach trees. Commercial growers in North Carolina can also use the NC State peach and nectarine pest management guide.

When to spray for borers in the trunk

Borer sprays work only on eggs and newly hatched larvae on the bark. Colorado State says that once larvae are inside the tree, insecticides are not effective. The goal is to coat the lower trunk so newly hatched larvae crawl through the residue.

Source	Suggested timing for peachtree borer
Colorado State (Colorado)	Around the first week of July; a second spray in early August if borers stay active
Clemson (South Carolina)	Annual trunk sprays during August
Mississippi State (Mississippi)	Two sprays 2 to 3 weeks apart, around mid-August and early September

CSU says permethrin or carbaryl products labeled for peachtree borer are the main options for backyard fruit trees. Clemson recommends spraying from the scaffold limbs to the ground so the bark is soaked and a small puddle forms at the base. Mississippi State notes that a single permethrin application will not give enough residual control.

Ways to cut down on spraying

Pick up dropped fruit. Clemson recommends collecting and destroying early-dropping fruit weekly, since it can hold curculio larvae, and cleaning up places where adults overwinter.
Bag the fruit. Clemson has tested fruit bags for home growers: protect fruit from bloom until bagging, then enclose thumbnail-sized green fruit (typically about three weeks after bloom) in a specialty bag until harvest.
Protect the trunk. Clemson says borers prefer wounds and rough bark. Avoid mower and trimmer damage, and keep trees vigorous.
Remove damaged wood. For lesser peachtree borer, Clemson suggests pruning out split or borer-damaged limbs and destroying the wood before adults emerge in April.

Clemson is frank that without well-timed sprays, it is common for insects and disease to ruin an entire backyard peach crop. If you would rather not spray, bagging and sanitation are your best tools.

Key takeaways

Identify the “worm” first: plum curculio and Oriental fruit moth damage fruit; peachtree borers attack the trunk base.
Never spray insecticides during bloom; start fruit-protection sprays at petal fall and repeat on a schedule.
Spray the lower trunk for borers in summer, when eggs are laid; sprays do not reach larvae already inside.
Pick up dropped fruit, consider fruit bags and protect the trunk from wounds.
Read and follow every product label, including the days-to-harvest interval.

Sources

Peach Insect Pests (HGIC 2210), Clemson Cooperative Extension
Disease and Insect Control for Homegrown Peaches and Plums, Mississippi State University Extension
Peachtree Borer, Colorado State University Extension
North Carolina Peach and Nectarine Disease and Pest Management Guide, NC State Extension

How to Spray Peach Trees for Worms